.app {
  width: 100%;
  height: 45px;
  background-color: #ccc;
}
.app .nav { 
  width: 1200px;
  margin: 0 auto ;
  height: 100%;
}
.app .nav li {
  float: left;
padding: 0 25px ;

line-height: 45px;

}
.app .nav  .active {
  background-color: red;
  color: #fff;
}
.app .nav li:hover {
  background-color: #fff;
  color: #000;
}
.app .nav .right {
  float: right;
  line-height: 45px;

}
.app .nav .right  span {
  cursor: pointer;
}
.app .nav .right  span:hover {
  color: red;
}
.banner {
  width: 1200px;
  height: 450px;
  margin: 0 auto;
  overflow: hidden;
}
.banner img {
  width: 100%;
  height: 100%;
}
@media screen and (max-width: 767px) {
  .nav {
      width: 100%;
  }
}
@media (min-width:768px) {  
}

@media (max-width: 992px) {  
  .app .nav { 
    width: 992px;
    margin: 0 auto ;
    height: 100%;
  }
}


@media (min-width: 1200px) {  }